GitHub user BryanCutler opened a pull request:

    https://github.com/apache/spark/pull/16782

    [SPARK-19348][PYTHON][WIP] PySpark keyword_only decorator is not thread-safe

    ## What changes were proposed in this pull request?
    The `@keyword_only` decorator in PySpark is not thread-safe.  It writes 
kwargs to a static class variable in the decorator, which is then retrieved 
later in the class method as `_input_kwargs`.  If multiple threads are 
constructing the same class with different kwargs, it becomes a race condition 
to read from the static class variable before it's overwritten.  See 
[SPARK-19348](https://issues.apache.org/jira/browse/SPARK-19348) for 
reproduction code.
    
    This change will write the kwargs to a member variable so that multiple 
threads can operate on separate instances without the race condition.  It does 
not protect against multiple threads operating on a single instance, but that 
is better left to the user to synchronize.
    
    ## How was this patch tested?
    WIP


You can merge this pull request into a Git repository by running:

    $ git pull https://github.com/BryanCutler/spark 
pyspark-keyword_only-threadsafe-SPARK-19348

Alternatively you can review and apply these changes as the patch at:

    https://github.com/apache/spark/pull/16782.patch

To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:

    This closes #16782
    
----
commit a15e9b0a78d86685d6b27ac4fdfa37161376b288
Author: Bryan Cutler <cutl...@gmail.com>
Date:   2017-02-02T23:01:45Z

    made a thread-safe addition to keyword_only decorator

commit 83bcce0c2fc33184579224fca18066dbf6891d26
Author: Bryan Cutler <cutl...@gmail.com>
Date:   2017-02-02T23:11:32Z

    remove blank line

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